In the manufacture of electric discharge lamps or devices which utilize an ionizable medium containing mercury, it is always necessary to exercise care in introducing the mercury into the lamp in order to avoid contamination. Some lamps such as the common fluorescent lamp operate with a saturated mercury vapor and contain mercury in excess of the quantity vaporized in operation. With such lamps, accuracy in dispensing the dose is not of cardinal importance. However with high intensity discharge lamps which operate with the mercury dose totally vaporized, accuracy is important because the vapor pressure in operation depends upon the quantity of mercury which was dispensed into the arc tube. In metal halide lamps which contain both mercury and one or more metal halides, accurate control of the mercury dose is even more important for the further reason that the color of the radiation emitted by the lamp depends upon the proportion of the various ingredients. To assure a lamp product which is constant in color and performance, accurate control of the mercury dose is essential. In the manufacture of miniature metal halide lamps, the quantity of mercury dispensed per lamp is less than in conventional size lamps. This means that in order to have the same relative accuracy, even greater precision must be used in measuring and dispensing the required charge.
An example of mercury dispensing or dosing apparatus currently used in electrical discharge lamp manufacture is described in U.S. Pat. No. 2,313,657 - Marshaus (1943) Apparatus for Feeding Mercury. I have found that the methods currently used are not suitable and the available equipment is not fast enough nor precise and accurate enough for use with high speed production equipment in the manufacture of low wattage high intensity discharge lamps.